The production of alcohols from synthesis gas, the common designation for mixtures of hydrogen, carbon monoxide and carbon dioxide, is a process which has been practiced since the early twentieth century. German inventors Mittasch, Schneider, Winkler, Fischer, Tropsch during the period 1915 through 1930 made many inventions relating to the production of methanol and hydrocarbons from carbon monoxide, hydrogen and carbon dioxide. These early processes differed very significantly from the more efficient, more specific processes of the present. For example, Davies et al., in U.S. Pat. No. 3,326,956 teach the manufacture of almost pure methanol from CO and hydrogen plus carbon dioxide using a copper oxide, zinc oxide and aluminum oxide catalyst. Furthermore, Stiles in U.S. Pat. No. 4,111,847 taught the preparation of methanol also from synthesis gas increasing the rate of production per unit volume of catalyst and minimizing the production of unwanted by-products such as methane, hydrocarbons and higher alcohols.
Presently, it is desirable to produce methanol together with selected and specific higher alcohols from CO and hydrogen in order to produce an alcohol mixture which can be added to gasolines to make the United States less dependent upon foreign crude imports as well as to improve the gasoline's anti-knock properties. When methanol in its pure form is added to gasoline there are many complications which can develop such as water being adsorbed by the gasoline and forming a two-phase layer in the gasoline tanks. This causes extreme motor and driving problems.
However, if there are present in the methanol which is added to the gasoline quantities of 10 to 50% of higher alcohols including ethanol, propanol and butanols then this separation of phases is not a problem. As a consequence much work has recently been done in an effort to simultaneously produce methanol and these selected higher alcohols. For example, Sugier et al., in U.S. Pat. No. 4,122,110 teach the use of a catalyst comprising copper, cobalt and optionally chromium, manganese, vanadium or iron and an alkali metal. The alkali metal is preferably lithium, sodium or potassium. The product of the synthesis includes methanol, ethanol, propanol, isopropanol and butanols. A companion patent GB No. 2,037,179 was granted in Great Britian which claims essentially the same features of the catalyst with the exception that alkali earths are included as an equivalency for the lithium, sodium and potassium. No mention is made of cesium or rubidium or mixtures of the foregoing with cesium and rubidium.
Bartley et al., in U.S. Pat. No. 4,235,798 teach a process whereby synthesis gas is converted to two carbon atom products such as ethanol, ethylene glycol and acetaldehyde using a catalyst comprising rhodium, lithium, potassium, cesium, or rubidium on SiO.sub.2. This process is extremely inefficient in that the quantities of methane which are simultaneously produced are equal to 22% up to 56% of the total carbon monoxide fed. Thus this is an extremely inefficient process and although it stipulates cesium and rubidium as alkali it contains none of the other typical ingredients of alcohols synthesis catalyst such as copper, zinc manganese, and alumina.
In another process for producing higher alcohols Universal Oil Products in British patent GB No. 2,049,673 teach the reacting of olefinic materials with CO and hydrogen using group 8 metals as catalysts. These metals of course include the iron group and the platinum group but no mention is made of the use of alkali metals to moderate the reaction.
Ball et al., in U.S. Pat. No. 4,327,190 teach the synthesis of oxygenated compounds from synthesis gas using a catalyst comprising rhodium and chromium on silica gel. No alkali is included in the catalyst composition. Snamprogetti teach in British Pat. No. 2,083,469 the conversion of synthesis gas to mixtures of methanol and higher alcohols. The catalyst employed in this reaction is zinc and chromium plus alkali metal which is taught to be preferably potassium. Hardman et al., teach in U.S. Pat. No. 4,298,354 that synthesis gas can be converted to methanol and higher alcohols over a catalyst comprising copper, thorium oxide and alkali metal with the alkali metal being preferably sodium.
It can be seen that there is much prior patent art in this field but cesium or rubidium are not mentioned in any sense approaching the disclosures of the invention taught herein.
Despite the foregoing background indicating the degree to which this subject has been exposed to research world-wide, there exist problems which must be corrected. One of the problems is the concommitant production of relatively large quantities of methane. The loss of valuable synthesis gas to methane is in itself a serious economic loss but it becomes even more serious when purging of the methane from the synthesis system. During the purging of this objectionable methane there is lost simultaneously at least the equivalent of two additional volumes and very likely more of valuable CO and hydrogen. Thus it becomes apparent that avoidance of methanation is an extremely critical item and is the subject of one of the improvements of the catalysts of of this invention. Furthermore, it is highly desirable to produce only those products which will be most effectively used when blending methanol and higher alcohols into the gasoline fraction. The invention later to be described will also achieve this characteristic. In other words, the present invention differs from the previously described prior art in that the new catalysts have compositions which differ from anything previously described, produce less methane and also produce larger quantities of higher alcohols of the desired identity.